Seabirds: Canaries in the mine or
elephants with wings?by Kate Waterhouse

In
this article, Kate Waterhouse summarises some recent seabird
research findings reported at the Hauraki Gulf Marine Park Seminar:
Taking Flight, held on 6 September 2017 at the Auckland Museum.

The Hauraki Gulf, Te Moana Nui a Toi, Tikapa Moana, is a global
seabird hotspot. And here, seabirds, forest birds, lizards and even
some marine ecosystems are recovering where rats and other predators
have been removed from islands and sanctuaries.

The Hauraki Gulf is a magnet for seabird researchers and those
learning how to protect breeding colonies.

All over the world, seabirds have been marginalised to the most
remote areas and islands. They have no defences, having evolved
without mammalian predators – so stopping predation in breeding
colonies is a global issue.

All eyes on New Zealand

The Hauraki Gulf is a magnet for seabird researchers and those
learning how to protect breeding colonies. Dr Andre Raine of the
Kaua’i Endangered Seabird Recovery Project in Hawaii told the 400
strong audience at the Auckland Museum that New Zealand is at the
forefront of new methods - including traps, island eradications,
fenced sanctuaries, translocation, and social attraction projects,
such as Tawharanui, where seabirds are breeding again. He described
Predator Free New Zealand as a globally significant goal.

Why is the Hauraki Gulf a global seabird hotspot?

The numbers tell the story – of the 10,400 species of birds
globally, only 359 are seabirds, around 20% of the world’s seabirds
have been recorded here (over 70 species), and 26 species of seabird
breed in the gulf ,with four endemic to the region (including the
black petrel (Procellaria parkinsoni), fairy tern (Sternula
nereis)
(our nation’s rarest bird) and the recently rediscovered New Zealand
storm petrel (Fregetta
maoriana)1.

About 70% of New Zealand’s territory is ocean and it’s easy to see
from submarine topography and oceanic currents, that upwellings and
convergence zones near New Zealand make our waters extremely
productive. So said illustrator Chris Gaskin, one of the founders of
the Northern New Zealand Seabird Trust (NNZST). Chris pointed out
that in the Hauraki Gulf, trevally, kahawai and other school fish
feed on krill – so it’s not surprising seabirds have become
concentrated here also.

Shapeshifters: Why seabirds are so amazing - across distance and the
air/water divide

Chris Gaskin explained that being able to locate food scattered over
vast areas of ocean is key to survival for all seabirds. Multiple
senses come into play when they do this – especially sight and
smell.

They
have extraordinary physiology – for example for gannets, terns and
gulls, sight and body shape define them. They can see very well
below water as well as above it, and can keep flying through air and
into the much denser water with ease. Some shearwaters can dive down
to 90 m. The titi/sooty shearwater (Puffinus griseusan) dive
into water, a medium 800 times denser than air, up to 92 m under
water, and for 90 seconds.

Matt Rayner, who with Gaskin, rediscovered the New Zealand storm
petrel, explained that the titi is able to achieve such feats by
storing oxygen in its muscles, not its lungs.

Chris Gaskin speaking at Taking Flight in June. Photo: S. Lee

Seabird
islands are transformed at night, the air is alive with thousands
and sometime millions of birds returning to burrows.

But seabirds must come to land to breed, whether it’s gannets on a
rock stack off the Broken Islands, or petrels in the forests of
Hauturu/Little Barrier, Aotea, or the Poor Knights. In the daytime
you can see gannets, shags and terns because they are active by day,
when most petrels and shearwaters are at sea, only returning to land
at night. Seabird islands are transformed at night, the air is alive
with thousands and sometime millions of birds returning to burrows.

On Hauturu the noise can be deafening – the equivalent of Auckland’s
population in Cook’s petrels (Pterodroma cookie) alone arrive
nightly. Before mammalian predators arrived and seabirds were lost,
this is what many of our forests would have been like.

The imperative to breed is what brings seabirds to land, but getting
back to sea can be tricky with many species, such as Buller’s
shearwaters, climbing trees to gain a platform to take off. A
seabird’s most difficult time in life is their first year – it is a
miracle time for many. Gaskin described a 35 g New Zealand storm
petrel – hatched in deep forest high on Hauturu, fed by parents for
two months before emerging and stretching over several nights. “It
might be raining, or windy, but eventually it must fly out through
the forest, down a valley and out to sea – a whole new world opens
before it... It has to find food - the right type of food, but its
body is fit for purpose, strong and waterproof enough to survive.
With each passing year its survival chances increase”.

Elephants with wings: Burrowing seabirds are ecosystem engineers

Dave Towns of the Auckland University of Technology (AUT) believes
burrowing seabirds are like “elephants with wings”. Seabirds in the
Hauraki Gulf are burrowing species which makes them ecosystem
engineers, just like elephants in the African savannah. On a seabird
island you will see what looks like elephant damage on the ground
and in the trees. They raise the nutrient content through excreting
guano and lower the pH level of the soil. Why is this important?

As Dr James Ross from Tawharanui Open Sanctuary points out, this
nutrient cycling process helps to restore ecosystems, on land and in
the ocean.

But just how big is the impact of seabirds? Ross went to Hauturu to
determine just how much guano is produced by one million Cook’s
petrels. Estimates were based on how long the birds are resident,
the altitude and guano production rates. The answer turned out to be
about 55 tonnes per year, the equivalent of about 50 kilograms per
hectare per year of fertiliser. Literature suggests that this
estimate is at the low end. Wedge-tailed shearwaters (Puffinus
pacificus) in the Pacific are thought to add 230 kilograms per
hectare – a very significant nutrient input to the ecosystem2!

The amazing effects on islands when seabirds do come back

So where do the nutrients go?

The answer is into both the forests and the sea. The benefits
seabirds bring flow to plants, trees, small reptiles and
invertebrates and nearby marine ecosystems. Comparing islands with
and without seabirds shows that the food webs of invertebrates are
much more complex on seabird islands than non-seabird islands. In
fact, according to Towns, they approach the most complex food webs
found anywhere.

Seabirds play an important role in the transfer of
marine-derived nutrients to land with resulting impacts on
terrestrial ecosystem productivity3.

Seabird islands have healthier marine environments too. AUT
researchers Rachel Buxton and Steph Borrell found unexpected results
in the intertidal and subtidal seaweed communities around seabird
islands studied. Species diversity is higher and three species
showed evidence of enrichment. Such a finding has implications for
the way we design our marine reserves. If seaweeds are healthier at
the base of the food chain, then other biodiversity will benefit
too.

How seabirds recolonise a place: the halo effect and social
attraction

When James Ross heard Chris Gaskin talk in 2010 about a grey-faced
petrel (Pterodroma macroptera) that he had found flying
around the Tawharanui Open Sanctuary, he decided to take action to
bring seabirds back to the peninsula. This goal proved to be a
challenge, as researcher Rachel Buxton outlined, but it shows what
is possible on Rakitu and other islands off Aotea’s coast in a very
short time, should rats and cats be removed.

Recolonisation is helped considerably by being near to a source
population of birds – because social cues are very important too.
Sound systems played seabird calls all night every night from
prominent headlands all over Tawharanui. Within months, they had
attracted diving petrels (Pelecanoides urinatrix), fluttering
shearwaters (Puffinus gavial) and non- target species. After
decades of farming, the soil at Tawharanui was very compacted, so
the team provided nest boxes as an alternative to burrows. Breeding
has been successful. About 350 birds have been banded and these
diving petrels and fluttering shearwaters may be the first mainland
breeding records in the gulf for many decades.

How long will it take for the elephants with wings to perform the
role of ecosystem engineers?

Elsewhere in the gulf, recolonisation is happening very rapidly,
with Pycroft’s petrel (Pterodroma pycrofti) now back on Great
Mercury three years after the removal of mammalian pests - the first
time in 800 years. Buxton and Borrell have also turned their
attention to how far seabirds will go to recolonise islands. The
answer may be up to 25 km from their natural home. The pair have
mapped ‘recruitment halos’ showing how rat-free island groups like
the Mokohinaus and Hen and Chickens can provide new colonisers for
neighbouring islands.

‘Recruitment halos’ showing how rat-free island groups like the
Mokohinaus and Hen and Chickens can provide new seabird colonisers
for neighbouring islands. (Source: R. Buxton and S. Borrell)

Aotea and Hauturu are on the outer limit of these halos and the
recruitment halo of the Mercury Islands is south of Aotea. Seabird
experts are confident that using the social attraction techniques
tested at Tawharanui (and elsewhere) will be successful. The
Mokohinau Islands sustain seven seabird species and Rakitu and the
north coast of Aotea sit squarely on the seabird highway.3

Can seabirds recover? What do they need from us?

AUT’s Steph Borrell has looked at the multiple challenges seabirds
face at sea and how seabirds recover following predator
eradications. On a rat island, seabird population growth never
reaches its maximum rate, although as soon as rats are gone, the
pressure reduces and seabird populations start to recover. Steph’s
work included 14 species of petrels and shearwaters (Procellariae)
and created a model for population growth in the absence of other
types of pressure i.e., optimal conditions. Seabirds generally have
long lifespans and low breeding rates which makes breeding success
very important to long term survival of a species.

...fisheries bycatch alone, sends most seabird species into decline
and pushes population growth below zero.

She added other threats to the model – plastic pollution, fisheries
impacts, and climate change. The results show that fisheries bycatch
alone, sends most seabird species into decline and pushes population
growth below zero. Climate change impacts are also variable,
although even a fractional adjustment for change in some climate
parameters means some populations will decline.

Tracking seabirds and ocean productivity

Seabirds
are following productivity in the oceans, say Dr Matt Rayner of
Auckland Museum and Dr Brendon Dumphy of University of Auckland. So
they have been looking at where seabirds go. From the gulf, it’s all
over the Pacific, connecting us culturally, spiritually and
genetically to other places – a spatial imprint they have been able
to obtain via geo-locators attached to seabirds. Rayner says it’s
clear that climate change is warming the gulf, but the east coast,
where many seabirds are breeding and feeding, has less temperature
‘headroom’ than the west coast. The team studied the diving petrel,
a species that migrates to the polar front in winter in 13-15 days
to follow ocean productivity. In the summer months, tracking showed
that Tiritiri Matangi-based birds and Mokohinau Island birds feed on
different things – plankton offshore (Mokes birds) and fish inshore
(Tiri birds). But the Mokohinau birds are more stressed - their
blood stressors are higher and they are lighter over time. The team
believes this is being driven by stronger and more frequent El Niño
seasons.

Last words

Seabird scientists know that the more we learn, the more we know how
much we don’t know. This raises the question of how close are we to
missing indications that some species might be about to go, and how
close were we to losing the New Zealand storm petrel?

Town concluded that the ecosystem engineering of seabirds is well
known - we can reinstate species by removing predators, and advance
our knowledge on natural re-colonisation. But how big we can get
when it comes to eradications depends on working on inhabited
islands with people. “If people engage in this process they may
themselves get to see elephants with wings.”

...how big we can get when it comes to eradications depends on
working on inhabited islands with people.

Dame Anne Salmondwent further, saying we cannot continue to
separate human activities from ecosystems. We’re all linked, and the
science of complex systems backs this up. If we think these things
are there to serve us, or are resources for our purposes, the
outcomes won’t be good for anyone.

As scientists at the seminar demonstrated, seabird islands support
significantly more life than those where seabirds have been eaten
out by predators. So without more focus on how to protect and expand
seabird breeding sites, we run the risk not only of losing birds to
extinction, but changing the fertility and biomass of islands
forever.